Amek M2500 console bus balancing
- Thread starter ilfungo
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jensenmann
Well-known member
You mean the 24track busses? The easiest way is to use impedance balancing. That means you wire the same resistor as used as output decoupling resistor on the output cards from the - to ground. That way the recieving gear sees the same impedance on both the + and - line. Any error signal induced will create the same current and thus will be canceled in the reciever input stage. That saves a lot of money, iron and copper compared to transformers.
If you want transformers for whatever reason then simply use a 600:600 ohm output type. Bigger core = less distortion, higher nickel content in the core = less distortion but also less max. level. Something like a Jensen JT-11 BMCF is an example of a good compromise for highest performance: MuMetal core (80% Nickel, hence low distortion) and huge core, hence high max. Level. If you want something that eats up your transients then look at smaller cores with higher nickel content. If you want distortion then look at low nickel content in the core.
If you want transformers for whatever reason then simply use a 600:600 ohm output type. Bigger core = less distortion, higher nickel content in the core = less distortion but also less max. level. Something like a Jensen JT-11 BMCF is an example of a good compromise for highest performance: MuMetal core (80% Nickel, hence low distortion) and huge core, hence high max. Level. If you want something that eats up your transients then look at smaller cores with higher nickel content. If you want distortion then look at low nickel content in the core.
Do you mean actually balancing mixing bus? or just balancing the outputs?ilfungo said:
The 24track busses.
I could try different configurations (impedance Balance,transformers,...)
My question is could the bus amp drive directly 600 ohm transformer?
I'm using 2 big Marinar transformers for the master bus and I love the sound, but I' ve upgraded the IC's with LME49720.
Thanks!!!
I could try different configurations (impedance Balance,transformers,...)
My question is could the bus amp drive directly 600 ohm transformer?
I'm using 2 big Marinar transformers for the master bus and I love the sound, but I' ve upgraded the IC's with LME49720.
Thanks!!!
It seems there is a language issue there. I guess you mean the multitrack outputs; naming them bus is improper IMO, cause bus are internal to the mixer. Converting bus to balanced is a major redesign and overhaul.ilfungo said:
So finally, it's the MT outputs you want to balance. It's difficult to say without a schemo. Tried to find it but no success. Some Amek decks use hybrid output stages, others simple one op-amp stage, but none of them seems really adequate for driving a 600 ohm load. However, you probably won't load the outputs with 600 ohms, are you? The Jensen xfmr loaded with 10k at the secondary should not reflect at the primary less than 2-3kohms, which any properly designed output stage should be capable of driving.
jensenmann
Well-known member
The multitrack output amps can easily drive output transformers. In fact the same cards are used as headphone amps (in my desk at least).
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If you have the schematics, would you be so kind as uploading them to the Technical Bulletin. The Amek section is rather poor. No copyright problems since the brand is extinct.jensenmann said:
jensenmann
Well-known member
I´d love to, but I have those schematics on paper only. It´s something like A1 format. Several people contacted me over the years reg. schematics and I always took pictures. Unfortunately it is not possible to get the entire schematic on a picture so that the resolution is good enough to read everything. I´ve attached a picture of the line driver card that we´re talking about, though.
Attachments
jensenmann
Well-known member
Exactly like this. If you want to get anal about LF distortion and phaseshift then you should add the same coupling cap to the new 47 Ohm resistor as is present in the + output (C6) of the card.
Too bad! Thanks anyway.jensenmann said:
Before shedding a lot of dough, what is your motivation?ilfungo said:
A) For short cable runs (less than 20 meters) balancing is not necessary if the destination is balanced.
B) Impedance balance is as good as transformer balanced if done well
c) Do you want the "sound" of transformers?
jensenmann
Well-known member
Yes.
Amek was using Sowter transformers in their broadcast versions of the M2500. But these desks had transformers at their inputs, not at the outputs.
Amek was using Sowter transformers in their broadcast versions of the M2500. But these desks had transformers at their inputs, not at the outputs.
